The present invention relates to the use of particular styrene-maleic anhydride copolymers and inorganic salt dispersant materials to achieve a reduction in the water demand of finely-divided solids in water. It relates particularly to this use as an improvement in the wet process production of portland cement.
It is known that copolymers of maleic anhydride and divinyl ether, ethylene, propylene butylene and isobutylene or mixtures of olefins and hexadiene-1,5 function as water-loss preventives in drilling fluids. See U.S. Pat. No. 3,157,599.
The above copolymers have also been employed with alkali metal compounds in preparing beneficated clay compositions for use in drilling fluids. U.S. Pat. No. 3,216,934 teaches the use of such copolymers with from about 1 to about 7 percent by weight of an alkali metal salt such as, for example, alkali metal carbonates, hypophosphites, oxalates, phosphates, silicates, sulfites and tartrates, to increase yields of clay. Similarly, U.S. Pat. No. 3,220,946 discloses the use of such maleic anhydride copolymers and certain alkali metal salts in clay benefication of sodium bentonites only. Salts selected from the group consisting of sodium formate, calcium formate, calcium acetate, sodium thiocyanate, sodium sulfate, magnesium sulfate, calcium sulfate, lithium sulfate and potassium sulfate are employed to provide a postulated synergistic response with the copolymer in changing the rheological properties of clay. Salts such as sodium chloride, sodium bicarbonate, calcium carbonate and calcium chloride, however, are taught as being ineffective for such uses.
It is also known that styrene-maleic anhydride copolymers are useful as water demand reducing agents in the wet process for producing portland cement. Such copolymers are employed in amounts from about 0.01 to about 0.1 weight percent. See U.S. Pat. No. 3,923,717.
A two-part study by the Portland Cement Association, Chicago, Ill., entitled "Slurry Thinners" (Part I, Clausen et al., May 1953; Part II by Dersnah, March 1955) discloses the evaluation of various inorganic salt dispersants and mixtures thereof with other surface active agents in reducing the water content of cement slurries in wet process applications.
Only the above Portland Cement Association Study and the U.S. Pat. No. 3,923,717 relate to the wet grinding process for making portland cement, wherein limestone and clay and, optionally, a small amount of iron oxide are ground in the presence of water to obtain a slurry of very fine particles. This slurry is then fed into a high temperature kiln where it is dried and calcined to form the clinker which is then ground to make portland cement. The water demand of the finely ground limestone-clay slurry is fairly high and ordinarily requires a relatively large proportion of water, for example, about 30-50% by weight, usually from about 25 to about 35 wt. %, to obtain a fluid, pumpable slurry. This limits the rate at which the slurry can be processed and fed to the kiln and it also requires a larger amount of fuel to dry and calcinate a given quantity of solids to the clinker stage.
Many substances with dispersant activity are available and have been tried in order to decrease the water demand of suspended inorganic solids in various high solids water suspensions or slurries for various applications. Most of these, particularly in the wet process for making portland cement, have proven relatively ineffective or undesirable for one reason or another. Complex phosphates are undesirable because they tend to hydrolyze at the warm temperatures developed during grinding and in storage of the slurry and because of the adverse effect of residual phosphate on the properties of the final portland cement product. Lignosulfonates have been tried for this use, but these require high addition levels for only marginal improvement. The also lose their activity rapidly during storage of the slurry. Many materials are also too expensive to be economically utilized in such operations.
We have now found, however, that the water demand of suspended inorganic solids necessary to make a pumpable slurry in the wet grinding process for making cement can be significantly reduced by use of water-demand reducing agent as described below.